As manufacturing techniques of VLSI semiconductor elements, processing techniques for densification and miniaturization of the semiconductor elements have been presently researched and developed. CMP (Chemical Mechanical Polishing) technique is one of the processing techniques like this. A flattening technique using CMP has become an essential technique for flattening interlayer insulating materials, forming STI (Shallow Trench Isolation), forming plugs, forming embedded metal wires (damascene step), or the like, in manufacturing steps of semiconductor elements. A CMP step (flattening step using a CMP technique) is generally performed by supplying a CMP polishing agent between a polishing pad (polishing cloth) and a material to be polished of a base and by polishing the material to be polished with the polishing pad.
Various polishing agents have been known as the CMP polishing agent used for CMP. When the CMP polishing agent is classified according to the kinds of abrasive grains (polishing particles), there have been known a ceria-based polishing agent comprising cerium oxide (ceria) particles, a silica-based polishing agent comprising silicon oxide (silica) particles, an alumina-based polishing agent comprising aluminum oxide (alumina) particles, a resin particle-based polishing agent comprising organic resin particles, or the like.
Incidentally, in recent years, achievement of further miniaturization of wires has been required in manufacturing steps of semiconductor elements, and polishing scratches generated during polishing have become a problem. More specifically, when polishing is performed using conventional polishing agents, generation of fine polishing scratches gives no problem as long as the size of the polishing scratches is smaller than the conventional wire width, but becomes a problem in the case where further miniaturization of wires is tried to be achieved.
For this problem, the average particle diameter of the abrasive grains comprised in the polishing agent is tried to be reduced. However, if the average particle diameter is reduced, the polishing rate is decreased due to a decrease in the mechanical action. It is extremely difficult to achieve both a polishing rate and polishing scratches in this manner. In response to this, polishing agents using abrasive grains including a hydroxide of a tetravalent metal element have been studied (for example, refer to the following Patent Literatures 1 to 4).
In CMP steps or the like for formation of STIs, polishing is performed for a laminated product including a substrate having an irregularity pattern, a stopper (polishing stop layer) disposed on the convex part of the substrate, and an insulating material (for example, silicon oxide) disposed on the substrate and the stopper so as to fill the concave part of the substrate. The polishing of the insulating material is stopped by the stopper during such a polishing. More specifically, the polishing of the insulating material is stopped at the stage where the stopper is exposed. This is because it is difficult to artificially control the polished amount of the insulating material (for example, the removed film thickness in the insulating film), and the polishing degree is controlled by polishing the insulating material until the stopper is exposed. In this case, it is necessary to increase polishing selectivity for insulating material with respect to stopper material (polishing rate ratio: polishing rate for insulating material/polishing rate for stopper material).
In response to the demand, a polishing agent comprising an additive has been known (for example, refer to the following Patent Literature 5). According to this technique, there is described polishing of silicon oxide using silicon nitride as a stopper material by a polishing agent comprising particles of a hydroxide of a tetravalent metal element and at least one of a cationic polymer and polysaccharide.
Silicon nitride is conventionally used as a stopper material, but polysilicon is increasingly used as the stopper material in recent years. In this case, it is necessary to further increase polishing selectivity for insulating material with respect to polysilicon. In response to the demand, a polishing agent comprising an additive has been known (for example, refer to the following Patent Literature 6).